William Muldoon was born in the village of Belfast , New York , in 1845 and joined the Union Army in 1861 to fight in the Civil War. He learned his wrestling in the Union camps between battles, and when the war ended he returned to New York City and joined the police force.

Buy Muldoon continued to wrestle on the side, and became a very popular attraction throughout the city. He eventually won acclaim as world champion in the Greco-Roman style of wrestling, and began barnstorming throughout the country. He was one of the first athletes to appear on a sports card, being in the popular Allen and Ginter card series of 1887.

After retiring from the ring, Muldoon became a highly respected trainer of athletes and opened a physical fitness farm. He also worked as trainer for the legendary world heavyweight boxing champion John L. Sullivan. Muldoon served as New York commissioner of sports for many years, and his biography, Muldoon: The Solid Man of Sports, was a popular sports book. He died in 1933 at the age of 88, one of the first legends in American sporting circles.